This invention generally relates to compressors, and more particularly to a portable, diesel-driven, microprocessor-based, centrifugal compressor.
Many modern industries, such as the pharmaceutical industry, the food processing industry, and the textile industry require "oil-free" compressed air. Two types of compressors which are capable of supplying oil-free compressed air are the dry-screw type compressor and the centrifugal compressor. The dry-screw type compressor and the centrifugal compressor each have respective advantages and disadvantages, however, at compressor outputs above 1000 cubic feet per minute (CFM), centrifugal compressors offer distinct advantages, such as better overall performance, a longer operating life, and better reliability. Despite the advantages of the centrifugal compressor, this type compressor has not been widely used in truly portable applications because of the complex design challenges associated with packaging a portable centrifugal compressor. To date, the most common type of portable, oil-free compressor has been the dry-screw compressor.
Water cooling systems are used with stationary centrifugal compressors because these cooling systems are extremely efficient, and usually lower the temperature of compressed air entering a second stage to temperatures near or below ambient temperature. Additionally, water cooling systems are able to cool final stage compressed air to temperatures well below the temperatures required by the industrial applications using the oil-free air. It is not uncommon for water cooling systems to cool final stage air to temperatures below 110.degree. to 120.degree. F. However, for a compressor to be truly portable, it must be air cooled, as opposed to liquid or water cooled, because water cooling typically is not available at remote locations. Also, in a portable compressor application, the machine must be able to operate in a wide range of ambient temperatures and altitudes. These portable compressors must be able to operate in temperatures ranging from minus 20.degree. F. to temperatures of approximately 120.degree. F.
To date, portable dry-screw compressors which have employed an air cooling system have only been able to cool final stage compressed air to temperatures of approximately 120.degree. F. above ambient temperature. However, such final stage compressed air temperatures typically exceed the temperature requirements of many of the modern industrial applications which require oil-free air. Therefore, in use, these air cooled dry-screw compressors must employ an additional stand alone aftercooler to supplement the main air cooling system of the dry-screw compressor. This of course is an additional expense for the user.
Centrifugal compressors rotate at extremely high speeds. For example, rotational speeds for a first stage impeller can be as high as 55,000 revolutions per minute (RPM), and rotational speeds for a second stage impeller can be as high as 66,000 RPM. Such rotational speeds, in combination with a nominal engine speed of approximately 1800 RPM, produce a gear ratio from engine speed to the first stage impeller speed of approximately 31:1, and a gear ratio from engine speed to the second stage impeller speed of approximately 38:1. These high gear ratios create high inertial forces within the compressor package. Additionally, engine torsional excitations which are caused by normal operation of a diesel engine, which is typically the prime mover of choice for a portable compressor, are an extremely disruptive force for the compressor gearing system and for compressor operation. Accordingly, a major deterrent which has heretofore thwarted commercial exploitation of a portable, diesel driven, centrifugal compressor has been an apparent industry wide inability to successfully couple a centrifugal compressor (air-end), having a high torsional inertia, to a diesel engine, which produces extreme engine torsional excitations.
Centrifugal compressor systems which include pneumatically controlled valves and components require high quality instrument air to be delivered to these pneumatic controlled components. Centrifugal compressors also require a source of sealing air. When a stationary centrifugal compressor package is installed within a manufacturing facility, typically, the instrument air and the seal air are provided from a source external to the centrifugal compressor package, such as by the manufacturing facility itself. However, in truly portable compressor applications at remote locations, facility or plant supplied instrument air typically is not available for use by the portable compressor to meet its instrument and seal air needs. Additionally, if such plant or facility supplied instrument air is available, often this externally supplied instrument air contains particulates, debris, and other foreign matter which clogs or otherwise damages the very sensitive pneumatically controlled components.
It is often necessary to unload or de-pressurize a compressor, such as for maintenance or during compressor shutdown. One method of unloading or de-pressurizing a compressor is by way of a blowoff valve. A fail-safe type blowoff valve is a spring loaded open type blowoff valve. Such a spring loaded open, blowoff valve is typically pneumatically controlled, and this valve must be pneumatically actuated to a closed position upon initial compressor start-up to pressurize or load the compressed air system. Presently, in compressed air systems which employ spring loaded open, pneumatically controlled, blowoff valves, upon initial compressor start-up, PG,6 these valves are actuated to a closed position by externally supplied instrument air, such as by plant or facility supplied instrument air. Accordingly, despite the laudable fail-safe benefits of employing a spring loaded open, pneumatically actuated blowoff valve in a compressed air system, these valves have not been employed in compressors to be used in remote, portable applications because there has not been an available method to pneumatically close these valves upon initial compressor start-up.
A portable compressor must have a lubricating oil system which is capable of operating in environments ranging from arctic conditions to desert conditions. While present portable compressor lubrication systems may have operated with some degree of success, these lubrication systems are replete with a multiplicity of deficiencies and shortcomings which have detracted from their usefulness.
The foregoing illustrates limitations known to exist in present portable compressors. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.